Which orbital class rocket (active or retired) has the highest thrust to weight ratio at liftoff?
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$\begingroup$ I thought this had been asked before, but if has, I could not find it. $\endgroup$– Organic MarbleSep 21, 2022 at 18:04
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3 Answers
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Seems like JAXA's SS-520 with launch mass of 2,600 kg and 14,600 kgF average thrust would have TWR of about 5.6
data found here
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1$\begingroup$ Video of launch here - youtu.be/OeW-Qqu9-8U?t=28 6 G acceleration? $\endgroup$ Sep 22, 2022 at 13:59
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$\begingroup$ The only SS-520 that successfully completed an orbital mission was fitted with a 78kg third stage. Additionally, the original paper reports a 14.2 ton average vacuum thrust, using some ideal rocket theory and the papers data the sea level thrust would be about 12.7 ton rounded up, i.e. 12.7/2.678 = 4.74 TWR (admittedly the paper is from 1982 and the orbital flight using the SS-520 was in 2018, so not entirely unlikely they improved the thrust) $\endgroup$– RubenSep 22, 2022 at 18:51
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$\begingroup$ To be fair, I cannot find any specification for the Mu-3H thrust data so it might as well be vacuum thrust too. Consequently assuming a similar correction for the Mu-3H thrust, the SS-520 used for the TRICOM-1R launch would still have the highest TWR $\endgroup$– RubenSep 22, 2022 at 18:55
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$\begingroup$ Ah, this is one of the Japanese ones which does its gravity turn at T-∞ :-D $\endgroup$ Sep 25, 2022 at 22:28
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$\begingroup$ @JörgWMittag Not really -∞, just T-(couple hours) when the erector is angled to the launch angle ;) $\endgroup$– SF.Sep 26, 2022 at 11:19
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I took the data from the JSR Launch Vehicle Database, available here. This includes take-off thrust and launch mass, so the Thrust-to-Weight Ratio was easily calculated. Unfortunately this list also includes many missiles and sounding rockets and I was too lazy too properly filter them with some other list of orbital class launch vehicles. However, eyeballing the list for orbital class launch vehicles with successful non-test missions, the Mu-3H seems to be the highest. It has a TWR of about 4.9, which certainly is quite high. Most of the Mu-family rockets have very high TWR.
After some further digging on the Mu-family I found a source in Japanese with sea-level thrusts and another (in English) with take-off mass for each configuration of the Mu-family rockets, which gives the following TWRs:
- 4.74 - M-3C
- 4.57 - M-3S/M-3H
- 4.52 - M-4S
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Assuming that the question refers to thrust to "total vehicle" weight ratio, I would opine that the ratio is determined by the mission. A heavy launch-to-orbit vehicle would be loaded to get the heaviest load to space and have a low thrust to weight ratio. An anti-missile missle would have a high thrust to weight ratio to accelerate rapidly and get to an approaching missile as far away from it's target as possible. I don't see any value in this parameter as a figure of merit.
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$\begingroup$ Using a high thrust to "total vehicle" weight ratio would result in a very rapid acceleration of the rocket and thus would require a stronger and heavier rocket structure. Also the payload structure should resist the rapid acceleration and would be heavier. $\endgroup$– UweSep 23, 2022 at 18:15
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$\begingroup$ Somebody asks: "Which animal runs the fastest?" You telling them: "I don't see any value in speed as a parameter for classifying animals" is not a useful answer $\endgroup$– RubenSep 24, 2022 at 15:21